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      <h1>VPatch 3.1</h1>
        <div> 
          <h2>Introduction</h2>
          <div>
          <p>VPatch allows to create a patch file to update previous versions 
            of your software. The GenPat utility generates the patch file. The 
            plug-in can use the patch to update a file. Using a patch, you can 
            reduce the download size of your updates because only the differences 
            between the files are included in the patch file.</p>
          </div>
          <h2>How to use</h2>
          <div>
          <h3>Generate the patch file</h3>
          <div>
          <p>Make sure you have the source file (original version) and the target 
            file (version to update to). For example, DATA.DTA (currently on user 
            system) and DATA_20.DTA (version 2.0 of this data file). Now call 
            the command line tool GenPat.exe:</p>
          <pre>
GENPAT oldfile.txt newfile.txt patch.pat
</pre>
          <p>Now, the patch will be generated, this will take some time.</p>
            <p>Using the /B=(BlockSize) parameter of the GenPat utility (put it 
              after the filenames), you can use a different block size. A smaller 
              block size may result in a smaller patch, but the generation will 
              take more time (the default blocksize is 64).</p>
            <p>If you have trouble using this command-line utility, you can download 
              a GUI (graphical user interface) for VPatch from its own website: 
              <a href="http://www.tibed.net/vpatch">http://www.tibed.net/vpatch</a>.</p>
          </div>
          <h3>Update the file during installation</h3>
          <div>
          <p>Use the VPatch plug-in to update a file using a patch file:</p>
          <pre>
vpatch::vpatchfile "patch.pat" "oldfile.txt" "temporary_newfile.txt"
</pre>
          <p>The result of the patch operating will be added to the stack and 
            can be one of the following texts:</p>
          <ul>
            <li>OK</li>
            <li>OK, new version already installed</li>
            <li>An error occurred while patching</li>
            <li>Patch data is invalid or corrupt</li>
            <li>No suitable patches were found</li>
          </ul>
            <p>Check <a href="../../Examples/VPatch/example.nsi">example.nsi</a> for an example. You 
              should check whether the stack string starts with &quot;OK&quot; 
              because then the patch has succeeded and you can rename &quot;temporary_newfile.txt&quot; 
              to &quot;oldfile.txt&quot; to replace the original, if you want.</p>
          </div>
          <h3>Multiple patches in one file</h3>
          <div>
          <p>GenPat appends a patch to the file you specified. If there is already 
            a patch for the same original file, with the same CRC/MD5, in the patch file,
            the patch will be replaced. For example, if you want to be able to upgrade
            version 1 and 2 to version 3, you can put a 1 &gt; 3 and 2 &gt; 3 patch in 
            one file.</p>
          <p>You can also put patches for different files in one patch file, for 
            example, a patch from file A version 1 to file A version 2 and a patch 
            from file B version 1 to file B version 2. Just call the plug-in multiple 
            times with the same patch file. It will automatically select the right 
            patch (based on the file CRC).</p>
          </div>
          <h3>Patch generator (GenPat) exit codes</h3>
          <div>
            <p>In version 3 the following exit codes (known as error levels in 
              the DOS period) can be returned by GenPat. GenPat will return an 
              exit code based on success of the patch generation. Here is a list 
              of the possible exit codes:</p>
            <table width="547" border="0" cellspacing="0" cellpadding="0">
              <tr> 
                <td><b>Exit code</b></td>
                <td><b>Description</b></td>
              </tr>
              <tr> 
                <td>0</td>
                <td>Success</td>
              </tr>
              <tr> 
                <td>1</td>
                <td>Arguments missing</td>
              </tr>
              <tr> 
                <td>2</td>
                <td>Other error</td>
              </tr>
              <tr>
                <td>3</td>
                <td>Source file already has a patch in specified patch file (ERROR), 
                  use /R switch to override</td>
              </tr>
            </table>
            <p>These exit codes can be useful when you generate patch files through 
              a NSIS script.</p>
        </div>
        </div>
        </div>
        <div>
          <h2>Source code</h2>
          <div>
          <p>Source code is available in the original package and in the SVN repository of NSIS.</p>
          <h3>NSIS plug-in (C++)</h3>
          <div>
          <p>The source of the NSIS plug-in that applies patches can be found 
            in the Source\Plugin folder.</p>
          </div>
          <h3>Patch Generator (C++)</h3>
          <div>
            <p>The most interesting part of VPatch, the actual patch generation 
              algorithm, can be found in Source\GenPat\PatchGenerator.cpp. The 
              header of that file contains a brief explanation of the algorithm 
              as well.</p>
          </div>
          <h3>User interface (Delphi)</h3>
          <div>
          <p>A user interface is included as well, which you will have to build 
            yourself because the GUI executable was too large to include. Besides 
            Borland Delphi 6 or higher (you can use the freely available Personal 
            edition), you will also need to install the <a href=
"http://www.delphi-gems.com">VirtualTreeView</a> component by Mike Lischke.</p>
          </div>
          </div>
          <h2>Version history</h2>
          <div>
          <ul>
            <li>3.1 
              <ul>
                <li>GenPat now compiles on POSIX platforms (MinGW/GCC), Visual 
                  C++ 6 and Borland C++.</li>
                <li>More test cases to verify functionality of GenPat.</li>
              </ul>
            </li>
            <li>3.0 
              <ul>
                <li><b>Final</b>: Updates to the GUI, installer</li>
                <li><b>RC8</b>: GenPat will now flag replacement of a patch (e.g. 
                  the source file has the same contents as a previous patch inside 
                  a patch file) as an error. You can specifically allow it using 
                  the /R switch. Added license to source files.</li>
                <li><b>RC7</b>: Fixed critical bug in GenPat with multiple patches 
                  in a single file. Fixed serious bug in stand-alone EXE runtime: 
                  process kept on running forever. Included case testing through 
                  a Python script to test common usage (and prevent bugs like 
                  the one in GenPat in the future).</li>
                <li><b>RC6</b>: Upgraded to non-beta compiler. Added /A switch 
                  to change block match limit and /O to deactivate the limit. 
                  Updated GUI to support the /O switch.</li>
                <li><b>RC4a to RC5a</b>: input block size is now checked for power 
                  of 2 and fixed if incorrect. When patch file does not yet exist, 
                  no longer forgets to create the header. No longer tries to allocate 
                  memory when there are no chunks. Fixed memory leaks.</li>
                <li>Target file date is now preserved inside a patch and restored 
                  on the user system.</li>
                <li>MD5 checksums are now used instead of CRC32 checksums, unless 
                  existing patches in a file already are in CRC32 mode.</li>
                <li>The patch generator, GenPat, has been completely rewritten 
                  in C++. It no longer needs to keep the entire files in memory, 
                  instead memory usage is a certain percentage of the source file 
                  size. The percentage is based on the block size, larger block 
                  sizes will reduce memory usage.</li>
                <li>All runtimes now share a common codebase, perform proper error 
                  checking and don't leave behind files if the input file was 
                  already up to date.</li>
                <li>Bug Fix: The patch generator algorithm no longer reduces to 
                  a quadratic runtime if there are many blocks with the same content 
                  in the files to patch.</li>
                <li>Bug Fix: The documentation of the command-line utilities was 
                  incorrect and no warnings would be given by the runtimes, causing 
                  the patch not to work (this does not apply to NSIS patches).</li>
              </ul>
            </li>
            <li>2.1 
              <ul>
                <li>Added argument checking and error handling to GenPat. Now 
                  returns exit codes as well to indicate success/failure (and 
                  the reason for failure). Only GenPat has changed in this version 
                  compared to 2.0 final.</li>
                <li>Bug Fix: GenPat no longer gives an Access Violation when attempting 
                  to patch a file smaller than 64 bytes into a file larger than 
                  64 bytes.</li>
              </ul>
            </li>
            <li>2.0 final 
              <ul>
                <li>Cleaned up source code for the patch generator, which is now 
                  included (this code is written in Borland Delphi 6 and compiles 
                  with the freely available Personal edition).</li>
              </ul>
            </li>
            <li>2.0 beta 2 
              <ul>
                <li>All new algorithm used in the patch generator: much faster 
                  (up to 90%) while using smaller block sizes (higher compression)</li>
                <li>Created a NSIS 2 plugin</li>
                <li>Works with small files</li>
                <li>Replaces existing patch in file if original file CRC is identical</li>
              </ul>
            </li>
          </ul>
          </div>
          <h2>Credits</h2>
          <div>
          <p>Written by Koen van de Sande<br />
            C plug-in initially by Edgewize, updated by Koen van de Sande<br />
            New documentation and example by Joost Verburg and Koen van de Sande</p>
          </div>
          <h2>License</h2>
          <div>
          <pre>
Copyright (C) 2001-2005 Koen van de Sande / Van de Sande Productions

This software is provided 'as-is', without any express or implied
warranty. In no event will the authors be held liable for any damages
arising from the use of this software.

Permission is granted to anyone to use this software for any purpose,
including commercial applications, and to alter it and redistribute
it freely, subject to the following restrictions:

1. The origin of this software must not be misrepresented; 
   you must not claim that you wrote the original software.
   If you use this software in a product, an acknowledgment in the
   product documentation would be appreciated but is not required.
2. Altered versions must be plainly marked as such,
   and must not be misrepresented as being the original software.
3. This notice may not be removed or altered from any distribution.
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